Towards quantum simulation of false vacuum decay

Phase transitions are in every single place, starting from water boiling to snowflakes melting, and from magnetic transitions in solids to cosmological phase transitions within the early universe. Particularly intriguing are quantum phase transitions that happen at temperatures near absolute zero and are pushed by quantum fairly than thermal fluctuations.

Researchers within the University of Cambridge studied properties of quantum phases and their transitions utilizing ultracold atoms in an optical lattice potential (shaped by a set of standing wave lasers). Typically, the transition from a Mott insulator (MI) to a superfluid (SF), which is ruled by the interaction of the atom-atom interactions and the hopping of atoms, is a steady transition, the place the system undergoes a easy steady change crossing the phase transition level.

However, many phase transitions are discontinuous, equivalent to water freezing to ice, or the transition thought to have triggered the inflation interval within the early universe. These are referred to as ‘first-order transitions’ and for example enable each phases to coexist—identical to ice blocks in a glass of water—and might result in hysteresis and metastability, the place a system stays caught in its authentic phase (the false vacuum) though the ground state has modified.

By resonantly shaking the place of the lattice potential, the researchers may couple or “mix” the primary two bands of the lattice. For the best parameters, this may excite the atoms from the bottom band into the primary excited band, the place they might type a brand new superfluid during which the atoms seem on the fringe of the band (see determine). Crucially, the transition from the unique Mott insulator within the lowest band to the ensuing staggered superfluid within the excited band may be first-order (discontinuous), as a result of the non-staggered order within the Mott insulator is incompatible with the staggered order of this superfluid—so the system has to decide on one. The researchers may straight observe the metastability and hysteresis related to this first-order transition by monitoring how briskly one phase adjustments into one other, or not. The findings are printed within the journal Nature Physics.

“We realized a very flexible platform where phase transitions could be tuned from continuous to discontinuous by changing the shaking strength. This demonstration opens up new opportunities for exploring the role of quantum fluctuations in first-order phase transitions, for instance, the false vacuum decay in the early universe,” mentioned first writer Dr. Bo Song from Cambridge’s Cavendish Laboratory. “It is really fascinating that we are on the road to cracking the mystery of the hot and dense early universe using such a cold and tiny atomic ensemble.”

“We are excited to enhance the scope of quantum simulators from condensed matter settings towards potential simulations of the early universe. While there clearly is a long way still to go, this work is an important first step,” added Professor Ulrich Schneider, who led the analysis on the Cavendish Laboratory. “This work also provides a testbed for exploring the spontaneous formation of spatial structures when a strongly interacting quantum system undergoes a discontinuous transition.”

“The underlying physics involves ideas that have a long history at the Cavendish, from Nevill Mott (on correlations) to Pyotr Kapitsa (on superfluidity), and even using shaking to effect dynamical control in a manner explained by Kapitsa but put to use in a way he would never have envisaged,” defined Professor Nigel Cooper, additionally from the Cavendish.